The present invention relates generally to the field of information processing by digital computers and, more particularly, to the processing and presentation of information by electronic spreadsheets.
Before computers, numerical analyses, particularly financial ones, were usually prepared on an accountant's columnar pad or spreadsheet, with pencil and calculator in hand. By organizing data into columns and rows, spreadsheets afford the rapid assimilation of information by a reader. The task of preparing a spreadsheet on paper, however, is not quite so fast. Instead, the process tends to be very slow, as each entry must be tediously calculated and entered into the spreadsheet. Since all calculations are the responsibility of the preparer, manually prepared spreadsheets are also prone to errors. Hence, preparation of spreadsheets by hand is slow, tedious, and unreliable.
With the advent of microcomputers, a solution was forthcoming in the form of "electronic spreadsheets." Better known simply as "spreadsheets," these software programs provide a computerized replacement for the traditional financial modeling tools: the accountant's columnar pad, pencil, and calculator. In some regards, spreadsheet programs are to those tools what wordprocessors are to typewriters. Spreadsheets offer dramatic improvements in ease of creating, editing, and using financial models.
A typical spreadsheet program configures the memory of a computer to resemble the column/row or grid format of an accountant's columnar pad, thus providing a visible calculator for a user. Because this "pad" exists dynamically in the computer's memory, however, it differs from paper pads in several important ways. Locations in the electronic spreadsheet, for example, must be communicated to the computer in a format which it can understand. A common scheme for accomplishing this is to assign a number to each row in a spreadsheet, and a letter to each column. To reference a location at column A and row 1 (i.e., the upper-lefthand corner), for example, the user types in "A1". In this manner, the spreadsheet defines an addressable storage location or "cell" at each intersection of a row with a column.
Data entry into an electronic spreadsheet occurs in much the same manner that information would be entered on an accountant's pad. After a screen cursor is positioned at a desired location, the user can enter alphanumeric information. Besides holding text and numeric information, however, spreadsheet cells can store special instructions or "formulas" specifying calculations to be performed on the numbers stored in spreadsheet cells. In this fashion, cell references can serve as variables in an equation, thereby allowing precise mathematical relationships to be defined between cells. The structure and operation of a spreadsheet program, including advanced functions such as functions and macros, are documented in the technical, trade, and patent literature. For an overview, see e.g., Cobb, S., Using Quattro Pro 2, Borland-Osborne/McGraw-Hill, 1990; and LeBlond, G. and Cobb, D., Using 1-2-3, Que Corp., 1985. The disclosures of each of the foregoing are hereby incorporated by reference.
Electronic spreadsheets offer many advantages over their paper counterparts. For one, electronic spreadsheets are much larger (i.e., hold more information) than their paper counterparts; electronic spreadsheets having thousands or even millions of cells are not uncommon. Spreadsheet programs also allow users to perform "what-if" scenarios. After a set of computational relationships has been entered into a worksheet, the spread of information can be recalculated using different sets of assumptions, with the results of each recalculation appearing almost instantaneously. Performing this operation manually, with paper and pencil, would require recalculating every relationship in the model with each change made. Thus, electronic spreadsheet systems were invented to solve "what-if" problems, that is, changing an input and seeing what happens to an output.
More recent implementations of these systems have added "solvers" or "optimizers." This adds goal-seeking functionality where a user can reverse the what-if process--deciding what value one wants an output to assume, with the system determining the appropriate input value(s). In a typical implementation, the user can set a target value at one cell, then specify both multiple input variables and multiple constraint cells. The optimizer finds all combinations of input values that achieve the target output without violating the constraints. Typically, a user employs such an optimizer to maximize or minimize an output cell (rather than aiming for a specific target value).
These backsolvers and optimizers are a good first step at improving the what-if process. To date, however, electronic spreadsheet systems have not been particularly adept at the process of actually managing the multitude of what-if scenarios, that is, multiple variations spawn from a single model. Since a given spreadsheet model is routinely created under a set of assumptions (e.g., level of sales, corporate tax rate, and the like), it is desirable to test the extremes of one's assumptions to ascertain the likely results. Although such "best case/worst case" analyses are commonly required by users, present-day systems have provided little or no tools for creating and managing such a multitude of scenarios. Instead, the user must resort to manually creating separate copies of the underlying model, with the user responsible for tracking any modifications made in the various copies. As this approach is undesirable at best, there is a great need for a better solution.